Prof. Osama El Masry

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Steam Condenser II
Mechanical Engineering Department ME332 Operation
and Management of Power Plants Prof. Osama A El
Masry

• Prof. Osama El Masry

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Steam Condenser Design

• Assumption while design heat exchanger
• The heat exchanger operates under steady-state
  conditions i.e., constant flow rates and fluid
  temperatures (at the inlet and within the
  exchanger) independent of time.
• Heat losses to or from the surroundings are
  negligible (i.e. the heat exchanger outside walls
  are adiabatic).
• There are no thermal energy sources or sinks in
  the exchanger walls or fluids, such as electric
  heating, chemical reaction, or nuclear processes.
• The temperature of each fluid is uniform over
  every cross section in counter flow and parallel
  flow exchangers. For a multipass exchanger, the
  foregoing statements apply to each pass depending
  on the basic flow arrangement of the passes the
  fluid is considered mixed or unmixed between
  passes as specified.

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• 5. Wall thermal resistance is distributed
  uniformly in the entire exchanger.
• 6.The phase change occurs at a constant
  temperature as for a single-component fluid at
  constant pressure the effective specific heat
  cpeff for the phase-changing fluid is infinity in
  this case, and hence Cmax m cpeff 00, where m
  is the fluid mass flow rate.
• 7. Longitudinal heat conduction in the fluids and
  in the wall is negligible.
• 8. The individual and overall heat transfer
  coefficients are constant (independent of
  temperature, time, and position) throughout the
  exchanger, including the case of phase changing
  fluids in assumption 6.
• 9. The specific heat of each fluid is constant
  throughout the exchanger, so that heat capacity
  rate on each side is treated as constant.

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• 10. . The heat transfer surface area A is
  distributed uniformly on each fluid side in a
  single-pass or multipass exchanger. In a
  multipass unit, the heat transfer surface area is
  distributed uniformly in each pass, although
  different passes can have different surface
  areas.
• 11. The velocity and temperature at the entrance
  of the heat exchanger on each fluids side are
  uniform over the flow cross section. There is no
  gross flow misdistribution at the inlet.
• 12. The fluid flow rate is uniformly distributed
  through the exchanger on each fluid side in each
  pass i.e., no passage-to-passage or
  viscosity-induced misdistribution occurs in the
  exchanger core. Also, no flow stratification,
  flow bypassing, or flow leakages occur in any
  stream. The flow condition is characterized by
  the bulk (or mean) velocity at any cross section

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Condenser Design
H.T. Calculation
Temperature Profile
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Heat Transfer
Dimensionless numbers and properties Prandalt
number Reynolds number Heat transfer
co-efficients Inside boundary of tube
Outside boundary of tube assume that outside
heat transfer co-efficient is 1.5 times the
inside heat transfer co-efficient Overall heat
transfer co-efficient
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Heat Transfer

• Q UA ?Tm
• ?Tm
• The overall H.T. coefficient U can also be
  expressed by the emperical Equation
• C1, C2 , C3 and C4 are obtained from the tables

U C1C2C3C4 vv
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Heat Transfer

Constants in Equation Constants in Equation Constants in Equation Constants in Equation
Tube outer diameter, in 3/4 7/8 1.0
C1 v m/s,U W/(m2 . k) 2777 2705 2582
Water Temp. oC 4 8 12 16 20 24 28 32 36 40
C2 0.58 0.64 0.72 0.79 0.86 0.93 1.0 1.04 1.08 1.12
Tube material Tube material 304 stainless steal Admiralty, Arsenic-copper Aluminum- Brass, Muntz metal Aluminum- Bronze, 90-10 Cu-Ni 70-30 Cu-Ni
C3 18 gauge 0.58 1.0 0.96 0.9 0.83
C3 17gauge 0.56 0.98 0.94 0.87 0.80
C3 16 gauge 0.54 0.96 0.91 0.84 0.76
C4 0.58 for clean tubes, less for algae or sludged tube C4 0.58 for clean tubes, less for algae or sludged tube C4 0.58 for clean tubes, less for algae or sludged tube C4 0.58 for clean tubes, less for algae or sludged tube C4 0.58 for clean tubes, less for algae or sludged tube C4 0.58 for clean tubes, less for algae or sludged tube C4 0.58 for clean tubes, less for algae or sludged tube
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• Surface area required
• AQ/ U ?Tm
• A (pd) x l x n
• Water calculation
• mw Q/cp (T2 T1)
• T2 T1?Ti -?To
• cpwater4.18 kJ/kg oK

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• Pressure drop

Pressure drop in condenser water box, m
(A)one-pass, (B)two-pass
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• Pressure drop

Pressure drop in condenser tubes m/m length of
tube
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Single-pass and Two-pass condensers
Single-pass Two-pass
Mass flowrate 2 m? m?
Power P 4 P
Temp. difference ?T 2 ?T
Condenser press. Pc gt Pc
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Example

• Design a condenser that would handle 1000 ton/h
  of 90 quality steam at 6 kPa and 120 ton/h of
  45oC drain water from FWH and 0.6 ton/h of 210
  oC drains from the steam jet ejector. Fresh
  cooling water is available at 20 oC.
• Solution
• H.T. calculation
• Select
• A two-pass condenser
• Type 304 stainless steel tubing
• Tubes 16 m in length, 7/8 OD, 18 BWG
• TTD 4 oC
• Inlet water velocity 2m/s

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• Heat load Q 1000 x 103 x (xhfg)120 x 103(h45oC
  -hf) 0.6 x 103(h210oC -hf)
• 1000 x 103 x (2174.4)120 x 103(36.9) 0.6 x
  103(746.2)
• 103x (21744004428447.7)2.175 x 109
  kJ/h604.16 x106 W
• ?Ti tsat-2036.2-2016.2 oC
• ?To 4 oC
• ?Tm(16.2-4)/ ln(16.2/4)12.2/1.3998.72 oC
• Q UA ?Tm (1)
• U C1C2C3C4 vv (2)
• From tables
• From tables U 2705x 0.86x 0.58x0.58 v21106.7
  W/m2. oC
• Total surface area62,604 m2
• For 7/8-in tubes surface area/m is 0.0698 m2 and
  cross-section area3.879cm2
• A /p d ltotal
• Total length of tubes 896,905 m

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• ltotal l x n
• Number of tubes56,056 tubes 28,028 tubes/pass
• Water calculation
• T2 T1?Ti -?To 12.2 oC
• For cpwater4.18 kJ/kg oK
• mw Q/cp (T2 T1) 604.16 x103/4.18x12.2
  11.8x103kg/s42,650 Ton/h
• check using Continuaty Equation
• Mass flow rate ? x v x A x n/210.87
  x103kg/s39,132 Ton/h

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• Pressure drop
• Pressure drop in water box 0.833 m0.0817 bar
• Pressure drop in tubes0.3 m/m length0.0294 bar
• Allow for 0.05 m thick tube sheet
• Each pass will have a length of 16.1 m
• Total pressure drop 0.0294 x 2 x 16.10.945 bar
• Total pressure drop in the condenser 0.9450.081
  71.029 bar
• Power m ?P/ ?1214.63 kW